Air and fuel supply system for combustion engine

ABSTRACT

A method of operating an internal combustion engine, including at least one cylinder and a piston slidable in the cylinder, may include supplying pressurized air from an intake manifold to an air intake port of a combustion chamber in the cylinder, selectively operating an air intake valve to open the air intake port to allow pressurized air to flow between the combustion chamber and the intake manifold substantially during a majority portion of a compression stroke of the piston, and operably controlling a fuel supply system to inject fuel into the combustion chamber after the intake valve is closed.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 10/143,908, filed May 14,2002, U.S. Pat. No. ______, the contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a combustion engine and, moreparticularly, to an air and fuel supply system for use with an internalcombustion engine.

BACKGROUND

An internal combustion engine may include one or more turbochargers forcompressing a fluid, which is supplied to one or more combustionchambers within corresponding combustion cylinders. Each turbochargertypically includes a turbine driven by exhaust gases of the engine and acompressor driven by the turbine. The compressor receives the fluid tobe compressed and supplies the compressed fluid to the combustionchambers. The fluid compressed by the compressor may be in the form ofcombustion air or an air/fuel mixture.

An internal combustion engine may also include a supercharger arrangedin series with a turbocharger compressor of an engine. U.S. Pat. No.6,273,076 (Beck et al., issued Aug. 14, 2001) discloses a superchargerhaving a turbine that drives a compressor to increase the pressure ofair flowing to a turbocharger compressor of an engine. In somesituations, the air charge temperature may be reduced below ambient airtemperature by an early closing of the intake valve.

Early or late closing of the intake valve, referred to as the “MillerCycle,” may reduce the effective compression ratio of the cylinder,which in turn reduces compression temperature, while maintaining a highexpansion ratio. Consequently, a Miller cycle engine may have improvedthermal efficiency and reduced exhaust emissions of, for example, oxidesof Nitrogen (NO_(x)). Reduced NO_(x)emissions are desirable. In aconventional Miller cycle engine, the timing of the intake valve closeis typically shifted slightly forward or backward from that of thetypical Otto cycle engine. For example, in the Miller cycle engine, theintake valve may remain open until the beginning of the compressionstroke.

While a turbocharger may utilize some energy from the engine exhaust,the series supercharger/turbocharger arrangement does not utilize energyfrom the turbocharger exhaust. Furthermore, the supercharger requires anadditional energy source.

The present invention is directed to overcoming one or more of theproblems as set forth above.

SUMMARY OF THE INVENTION

According to one exemplary aspect of the invention, a method ofoperating an internal combustion engine, including at least one cylinderand a piston slidable in the cylinder, is provided. The method mayinclude supplying pressurized air from an intake manifold to an airintake port of a combustion chamber in the cylinder, selectivelyoperating an air intake valve to open the air intake port to allowpressurized air to flow between the combustion chamber and the intakemanifold substantially during a majority portion of a compression strokeof the piston, and operably controlling a fuel supply system to injectfuel into the combustion chamber after the intake valve is closed.

According to another exemplary aspect of the invention, a variablecompression ratio internal combustion engine may include an engine blockdefining at least one cylinder, a head connected with the engine block,wherein the head includes an air intake port and an exhaust port, and apiston slidable in each cylinder. A combustion chamber may be defined bythe head, the piston, and the cylinder. The engine may include an airintake valve controllably movable to open and close the air intake port,an air supply system including at least one turbocharger fluidlyconnected to the air intake port, and a fuel supply system operable tocontrollably inject fuel into the combustion chamber at a selectedtiming. A variable intake valve closing mechanism may be configured tokeep the intake valve open by selective actuation of the variable intakevalve closing mechanism.

According to yet another exemplary aspect of the invention,a method ofoperating an internal combustion engine, including at least one cylinderand a piston slidable in the cylinder, is provided. The method mayinclude imparting rotational movement to a first turbine and a firstcompressor of a first turbocharger with exhaust air flowing from anexhaust port of the cylinder, and imparting rotational movement to asecond turbine and a second compressor of a second turbocharger withexhaust air flowing from an exhaust duct of the first turbocharger. Themethod may also include compressing air drawn from atmosphere with thesecond compressor, compressing air received from the second compressorwith the first compressor, and supplying pressurized air from the firstcompressor to an air intake port of a combustion chamber in the cylindervia an intake manifold. The method also includes controllably operatinga fuel supply system to inject fuel directly into the combustionchamber, and selectively operating an air intake valve to open the airintake port to allow pressurized air to flow between the combustionchamber and the intake manifold during a portion of a compression strokeof the piston.

According to still another exemplary aspect of the invention, a methodof controlling an internal combustion engine having a variablecompression ratio is provided. The engine may have a block defining acylinder, a piston slidable in the cylinder, a head connected with theblock, and the piston, the cylinder, and the head defining a combustionchamber. The method may include pressurizing air, supplying the air toan intake manifold, maintaining fluid communication between thecombustion chamber and the intake manifold during a portion of an intakestroke and through a predetermined portion of a compression stroke, andsupplying a pressurized fuel directly to the combustion chamber during aportion of an combustion stroke.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several exemplary bodiments ofthe invention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 is a combination diagrammatic and schematic illustration of anexemplary air supply system for an internal combustion engine inaccordance with the invention;

FIG. 2 is a combination diagrammatic and schematic illustration of anexemplary engine cylinder in accordance with the invention;

FIG. 3 is a diagrammatic sectional view of the exemplary engine cylinderof FIG. 2;

FIG. 4 is a graph illustrating an exemplary intake valve actuation as afunction of engine crank angle in accordance with the present invention;

FIG. 5 is a graph illustrating an exemplary fuel injection as a functionof engine crank angle in accordance with the present invention;

FIG. 6 is a combination diagrammatic and schematic illustration ofanother exemplary air supply system for an internal combustion engine inaccordance with the invention; and

FIG. 7 is a combination diagrammatic and schematic illustration of yetanother exemplary air supply system for an internal combustion engine inaccordance with the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Referring to FIG. 1, an exemplary air supply system 100 for an internalcombustion engine 110, for example, a four-stroke, diesel engine, isprovided. The internal combustion engine 110 includes an engine block111 defining a plurality of combustion cylinders 112, the number ofwhich depends upon the particular application. For example, a 4-cylinderengine would include four combustion cylinders, a 6-cylinder enginewould include six combustion cylinders, etc. In the exemplary embodimentof FIG. 1, six combustion cylinders 112 are shown. It should beappreciated that the engine 110 may be any other type of internalcombustion engine, for example, a gasoline or natural gas engine.

The internal combustion engine 110 also includes an intake manifold 114and an exhaust manifold 116. The intake manifold 114 provides fluid, forexample, air or a fuel/air mixture, to the combustion cylinders 112. Theexhaust manifold 116 receives exhaust fluid, for example, exhaust gas,from the combustion cylinders 112. The intake manifold 114 and theexhaust manifold 116 are shown as a single-part construction forsimplicity in the drawing. However, it should be appreciated that theintake manifold 114 and/or the exhaust manifold 116 may be constructedas multi-part manifolds, depending upon the particular application.

The air supply system 100 includes a first turbocharger 120 and mayinclude a second turbocharger 140. The first and second turbochargers120, 140 may be arranged in series with one another such that the secondturbocharger 140 provides a first stage of pressurization and the firstturbocharger 120 provides a second stage of pressurization. For example,the second turbocharger 140 may be a low pressure turbocharger and thefirst turbocharger 120 may be a high pressure turbocharger. The firstturbocharger 120 includes aiturbine 122 and a compressor 124. Theturbine 122 is fluidly connected to the exhaust manifold 116 via anexhaust duct 126. The turbine 122 includes a turbine wheel 128 carriedby a shaft 130, which in turn may be rotatably carried by a housing 132,for example, a single-part or multi-part housing. The fluid flow pathfrom the exhaust manifold 116 to the turbine 122 may include a variablenozzle (not shown) or other variable geometry arrangement adapted tocontrol the velocity of exhaust fluid impinging on the turbine wheel128.

The compressor 124 includes a compressor wheel 134 carried by the shaft130. Thus, rotation of the shaft 130 by the turbine wheel 128 in turnmay cause rotation of the compressor wheel 134.

The first turbocharger 120 may include a compressed air duct 138 forreceiving compressed air from the second turbocharger 140 and an airoutlet line 152 for receiving compressed air from the compressor 124 andsupplying the compressed air to the intake manifold 114 of the engine110. The first turbocharger 120 may also include an exhaust duct 139 forreceiving exhaust fluid from the turbine 122 and supplying the exhaustfluid to the second turbocharger 140.

The second turbocharger 140 may include a turbine 142 and a compressor144. The turbine 142 may be fluidly connected to the exhaust duct 139.The turbine 142 may include a turbine wheel 146 carried by a shaft 148,which in turn may be rotatably carried by the housing 132. Thecompressor 144 may include a compressor wheel 150 carried by the shaft148. Thus, rotation of the shaft 148 by the turbine wheel 146 may inturn cause rotation of the compressor wheel 150.

The second turbocharger 140 may include an air intake line 136 providingfluid communication between the atmosphere and the compressor 144. Thesecond turbocharger 140 may also supply compressed air to the firstturbocharger 120 via the compressed air duct 138. The secondturbocharger 140 may include an exhaust outlet 154 for receiving exhaustfluid from the turbine 142 and providing fluid communication with theatmosphere. In an embodiment, the first turbocharger 120 and secondturbocharger 140 may be sized to provide substantially similarcompression ratios. For example, the first turbocharger 120 and secondturbocharger 140 may both provide compression ratios of between 2 to 1and 3 to 1, resulting in a system compression ratio of at least 4:1 withrespect to atmospheric pressure. Alternatively, the second turbocharger140 may provide a compression ratio of 3 to 1 and the first turbocharger120 may provide a compression ratio of 1.5 to 1, resulting in a systemcompression ratio of 4.5to 1 with respect to atmospheric pressure.

The air supply system 100 may include an air cooler 156, for example, anaftercooler, between the compressor 124 and the intake manifold 114. Theair cooler 156 may extract heat from the air to lower the intakemanifold temperature and increase the air density. Optionally, the airsupply system 100 may include an additional air cooler 158, for example,an intercooler, between the compressor 144 of the second turbocharger140 and the compressor 124 of the first turbocharger 120. Alternatively,the air supply system 100 may optionally include an additional aircooler (not shown) between the air cooler 156 and the intake manifold114. The optional additional air cooler may further reduce the intakemanifold temperature.

Referring now to FIG. 2, a cylinder head 211 may be connected with theengine block 111. Each cylinder 112 in the cylinder head 211 may beprovided with a fuel supply system 202. The fuel supply system 202 mayinclude a fuel port 204 opening to a combustion chamber 206 within thecylinder 112. The fuel supply system 202 may inject fuel, for example,diesel fuel, directly into the combustion chamber 206.

The cylinder 112 may contain a piston 212 slidably movable in thecylinder. A crankshaft 213 may be rotatably disposed within the engineblock 111. A connecting rod 215 may couple the piston 212 to thecrankshift 213 so that sliding motion of the piston 212 within thecylinder 112 results in rotation of the crankshaft 213. Similarly,rotation of the crankshaft 213 results in a sliding motion of the piston212. For example, an uppermost position of the piston 212 in thecylinder 112 corresponds to a top dead center position of the crankshaft213, and a lowermost position of the piston 212 in the cylinder 112corresponds to a bottom dead center position of the crankshaft 213.

As one skilled in the art will recognize, the piston 212 in aconventional, four-stroke engine cycle reciprocates between theuppermost position and the lowermost position during a combustion (orexpansion) stroke, an exhaust stroke, and intake stroke, and acompression stroke. Meanwhile, the crankshaft 213 rotates from the topdead center position to the bottom dead center position during thecombustion stroke, from the bottom dead center to the top dead centerduring the exhaust stroke, from top dead center to bottom dead centerduring the intake stroke, and from bottom dead center to top dead centerduring the compression stroke. Then, the four-stroke cycle begins again.Each piston stroke correlates to-about 180° of crankshaft rotation, orcrank angle. Thus, the combustion stroke may begin at about 0° crankangle, the exhaust stroke at about 180°, the intake stroke at about360°, and the compression stroke at about 540 °.

The cylinder 112 may include at least one intake port 208 and at leastone exhaust port 210, each opening to the combustion chamber 206. Theintake port 208 may be opened and closed by an intake valve assembly214, and the exhaust port 210 may be opened and closed by an exhaustvalve assembly 216. The intake valve assembly 214 may include, forexample, an intake valve 218 having a head 220 at a first end 222, withthe head 220 being sized and arranged to selectively close the intakeport 208. The second end 224 of the intake valve 218 may be connected toa rocker arm 226 or any other conventional valve-actuating mechanism.The intake valve 218 may be movable between a first position permittingflow from the intake manifold 114 to enter the combustion cylinder 112and a second position substantially blocking flow from the intakemanifold 114 to the combustion cylinder 112. A spring 228 may bedisposed about the intake valve 218 to bias the intake valve 218 to thesecond, closed position.

A camshaft 232 carrying a cam 234 with one or more lobes 236 may bearranged to operate the intake valve assembly 214 cyclically based onthe configuration of the cam 234, the lobes 236, and the rotation of thecamshaft 232 to achieve a desired intake valve timing. The exhaust valveassembly 216 may be configured in a manner similar to the intake valveassembly 214 and may be operated by one of the lobes 236 of the cam 234.In an embodiment, the intake lobe 236 may be configured to operate theintake valve 218 in a conventional Otto or diesel cycle, whereby theintake valve 218 moves to the second position from between about 10°before bottom dead center of the intake stroke and about 10° afterbottom dead center of the compression stroke. Alternatively, the intakevalve assembly 214 and/or the exhaust valve assembly 216 may be operatedhydraulically, pneumatically, electronically, or by any combination ofmechanics, hydraulics, pneumatics, and/or electronics.

The intake valve assembly 214 may include a variable intake valveclosing mechanism 238 structured and arranged to selectively interruptcyclical movement of and extend the closing timing of the intake valve218. The variable intake valve closing mechanism 238 may be operatedhydraulically, pneumatically, electronically, mechanically, or anycombination thereof. For example, the variable intake valve closingmechanism 238 may be selectively operated to supply hydraulic fluid, forexample, at a low pressure or a high pressure, in a manner to resistclosing of the intake valve 218 by the bias of the spring 228. That is,after the intake valve 218 is lifted, i.e., opened, by the cam 234, andwhen the cam 234 is no longer holding the intake valve 218 open, thehydraulic fluid may hold the intake valve 218 open for a desired period.The desired period may change depending on the desired performance ofthe engine 110. Thus, the variable intake valve closing mechanism 238enables the engine 110 to operate under a conventional Otto or dieselcycle or under a variable late-closing Miller cycle.

As shown in FIG. 4, the intake valve 218 may begin to open at about 360°crank angle, that is, when the crankshaft 213 is at or near a top deadcenter position of an intake stroke 406. The closing of the intake valve218 may be selectively varied from about 540° crank angle, that is, whenthe crank shaft is at or near a bottom dead center position of acompression stroke 407, to about 650° crank angle, that is, about 70°before top center of the combustion stroke 508. Thus, the intake valve218 may be held open for a majority portion of the compression stroke407, that is, for the first half of the compression stroke 407 and aportion of the second half of the compression stroke 407.

The fuel supply system 202 may include a fuel injector assembly 240, forexample, a mechanically-actuated, electronically-controlled unitinjector, in fluid communication with a common fuel rail 242.Alternatively, the fuel injector assembly 240 may be any common railtype injector and may be actuated and/or operated hydraulically,mechanically, electrically, piezo-electrically, or any combinationthereof. The common fuel rail 242 provides fuel to the fuel injectorassembly 240 associated with each cylinder 112. The fuel injectorassembly 240 may inject or otherwise spray fuel into the cylinder 112via the fuel port 204 in accordance with a desired timing.

A controller 244 may be electrically connected to the variable intakevalve closing mechanism 238 and/or the fuel injector assembly 240. Thecontroller 244 may be configured to control operation of the variableintake valve closing mechanism 238 and/or the fuel injector assembly 240based-on one or more engine conditions, for example, engine speed, load,pressure, and/or temperature in order to achieve a desired engineperformance. It should be appreciated that the functions of thecontroller 244 may be performed by a single controller or by a pluralityof controllers. Similarly, spark timing in a natural gas engine mayprovide a similar function to fuel injector timing of a compressionignition engine.

Referring now to FIG. 3, each fuel injector assembly 240 may beassociated with an injector rocker arm 250 pivotally coupled to a rockershaft 252. Each fuel injector assembly 240 may include an injector body254, a solenoid 256, a plunger assembly 258, and an injector tipassembly 260. A first end 262 of the injector rocker arm 250 may beoperatively coupled to the plunger assembly 258. The plunger assembly258 may be biased by a spring 259 toward the first end 262 of theinjector rocker arm 250 in the general direction of arrow 296.

A second end 264 of the injector rocker arm 250 may be operativelycoupled to a camshaft 266. More specifically, the camshaft 266 mayinclude a cam lobe 267 having a first bump 268 and a second bump 270.The camshafts 232, 266 and their respective lobes 236, 267 may becombined into a single camshaft (not shown) if desired. The bumps 268,270 may be moved into and out of contact with the second end 264 of theinjector rocker arm 250 during rotation of the camshaft 266. The bumps268, 270 may be structured and arranged such that the second bump 270may provide a pilot injection of fuel at a predetermined crank anglebefore the first bump 268 provides a main injection of fuel. It shouldbe appreciated that the cam lobe 267 may have only a first bump 268 thatinjects all of the fuel per cycle.

When one of the bumps 268, 270 is rotated into contact with the injectorrocker arm 250, the second end 264 of the injector rocker arm 250 isurged in the general direction of arrow 296. As the second end 264 isurged in the general direction of arrow 296, the rocker arm 250 pivotsabout the rocker shaft 252 thereby causing the first end 262 to be urgedin the general direction of arrow 298. The force exerted on the secondend 264 by the bumps 268, 270 is greater in magnitude than the biasgenerated by the spring 259, thereby causing the plunger assembly 258 tobe likewise urged in the general direction of arrow 298. When thecamshaft 266 is rotated beyond the maximum height of the bumps 268, 270,the bias of the spring 259 urges the plunger assembly, 258 in thegeneral direction of arrow 296. As the plunger assembly 258 is urged inthe general direction of arrow 296, the first end 262 of the injectorrocker arm 250 is likewise urged in the general direction of arrow 296,which causes the injector rocker arm 250 to pivot about the rocker shaft252 thereby causing the second end 264 to be urged in the generaldirection of arrow 298.

The injector body 254 defines a fuel port 272. Fuel, such as dieselfuel, may be drawn or otherwise aspirated into the fuel port 272 fromthe fuel rail 242 when the plunger assembly 258 is moved in the generaldirection of arrow 296. The fuel port 272 is in fluid communication witha fuel valve 274 via a first fuel channel 276. The fuel valve 274 is, inturn. in fluid communication with a plunger chamber 278 via a secondfuel channel 280.

The solenoid 256 may be electrically coupled to the controller 244 andmechanically coupled to the fuel valve 274. Actuation of the solenoid256 by a signal from the controller 244 may cause the fuel valve 274 tobe switched from an open position to a closed position. When the fuelvalve 274 is positioned in its open position, fuel may advance from thefuel port 272 to the plunger chamber 278, and vice versa. However, whenthe fuel valve 274 is positioned in its closed positioned, the fuel port272 is isolated from the plunger chamber 278.

The injector tip assembly 260 may include a check valve assembly 282.Fuel may be advanced from the plunger chamber 278, through an inletorifice 284, a third fuel channel 286, an outlet orifice 288, and intothe cylinder 112 of the engine 110.

Thus, it should be appreciated that when one of the bumps 268, 270 isnot in contact with the injector rocker arm 16, the plunger assembly 258is urged in the general direction of arrow 296 by the spring 259 therebycausing fuel to be drawn into the fuel port 272 which in turn fills theplunger chamber 278 with fuel. As the camshaft 266 is further rotated,one of the bumps 268, 270 is moved into contact with the rocker arm 250,thereby causing the plunger assembly 258 to be urged in the generaldirection of arrow 298. If the controller 244 is not generating aninjection signal, the fuel valve 274 remains in its open position,thereby causing the fuel which is in the plunger chamber 278 to bedisplaced by the plunger assembly 258 through the fuel port 272.However, if the controller 244 is generating an injection signal, thefuel valve 274 is positioned in its closed position thereby isolatingthe plunger chamber 278 from the fuel port 272. As the plunger assembly258 continues to be urged in the general direction of arrow 298 by thecamshaft 266, fluid pressure within the fuel injector assembly 240increases. At a predetermined pressure magnitude, for example, at about5500 psi (38 MPa), fuel is injected into the cylinder 112. Fuel willcontinue to be injected into the cylinder 112 until the controller 244signals the solenoid 256 to return the fuel valve 274 to its openposition.

As shown in the exemplary graph of FIG. 5, the pilot injection of fuelmay commence when the crankshaft 213 is at about 675° crank angle, thatis, about 45° before top dead center of the compression stroke 407. Themain injection of fuel may occur when the crankshaft 213 is at about710° crank angle, that is, about 10° before top dead center of thecompression stroke 407 and about 45° after commencement of the pilotinjection. Generally, the pilot injection may commence when thecrankshaft 213 is about 40-50° before top dead center of the compressionstroke 407 and may last for about 10-15° crankshaft rotation. The maininjection may commence when the crankshaft 213 is between about 10°before top dead center of the compression stroke 407 and about 12° aftertop dead center of the combustion stroke 508. The main injection maylast for about 20-45° crankshaft rotation.

FIG. 6 is a combination diagrammatic and schematic illustration of asecond exemplary air supply system 300 for the internal combustionengine 110. The air supply system 300 may include a turbocharger 320,for example, a high-efficiency turbocharger capable of producing atleast about a 4 to 1 compression ratio with respect to atmosphericpressure. The turbocharger 320 may include a turbine 322 and acompressor 324. The turbine 322 may be fluidly connected to the exhaustmanifold 116 via an exhaust duct 326. The turbine 322 may include aturbine wheel 328 carried by a shaft 330, which in turn may be rotatablycarried by a housing 332, for example, a single-part or multi-parthousing. The fluid flow path from the exhaust manifold 116 to theturbine 322 may include a variable nozzle (not shown), which may controlthe velocity of exhaust fluid impinging on the turbine wheel 328.

The compressor 324 may include a compressor wheel 334 carried by theshaft 330. Thus, rotation of the shaft 330 by the turbine wheel 328 inturn may cause rotation of the compressor wheel 334. The turbocharger320 may include an air inlet 336 providing fluid communication betweenthe atmosphere and the compressor 324 and an air outlet 352 forsupplying compressed air to the intake manifold 114 of the engine 110.The turbocharger 320 may also include an exhaust outlet 354 forreceiving exhaust fluid from the turbine 322 and providing fluidcommunication with the atmosphere.

The air supply system 300 may include an air cooler 356 between thecompressor 324 and the intake manifold 114. Optionally, the air supplysystem 300 may include an additional air cooler (not shown) between theair cooler 356 and the intake manifold 114.

FIG. 7 is a combination diagrammatic and schematic illustration of athird exemplary air supply system 400 for the internal combustion engine110. The air supply system 400 may include a turbocharger 420, forexample, a turbocharger 420 having a turbine 422 and two compressors424, 444. The turbine 422 may be fluidly connected to the exhaustmanifold 116 via an inlet duct 426. The turbine 422 may include aturbine wheel 428 carried by a shaft 430, which in turn may be rotatablycarried by a housing 432, for example, a single-part or multi-parthousing. The fluid flow path from the exhaust manifold 116 to theturbine 422 may include a variable nozzle (not shown), which may controlthe velocity of exhaust fluid impinging on the turbine wheel 428.

The first compressor 424 may include a compressor wheel 434 carried bythe shaft 430, and the second compressor 444 may include a compressorwheel 450 carried by the shaft 430. Thus, rotation of the shaft 430 bythe turbine, wheel 428 in turn may cause rotation of the first andsecond compressor wheels 434, 450. The first and second compressors424,444 may provide first and second stages of pressurization,respectively.

The turbocharger 420 may include an air intake line 436 providing fluidcommunication between the atmosphere and the first compressor 424 and acompressed air duct 438 for receiving compressed air from the firstcompressor 424 and supplying the compressed air to the second compressor444. The turbocharger 420 may include an air outlet line 452 forsupplying compressed air from the second compressor 444 to the intakemanifold 114 of the engine 110. The turbocharger 420 may also include anexhaust outlet 454 for receiving exhaust fluid from the turbine 422 andproviding fluid communication with the atmosphere.

For example, the first compressor 424 and second compressor 444 may bothprovide compression ratios of between 2 to 1 and 3 to 1, resulting in asystem compression ratio of at least 4:1 with respect to atmosphericpressure. Alternatively, the second compressor 444 may provide acompression ratio of 3 to 1 and the first compressor 424 may provide acompression ratio of 1.5 to 1, resulting in a system compression ratioof 4.5 to 1 with respect to atmospheric pressure.

The air supply system 400 may include an air cooler 456 between thecompressor 424 and the intake manifold 114. Optionally, the air supplysystem 400 may include an additional air cooler 458 between the firstcompressor 424 and the second compressor 444 of the turbocharger 420.Alternatively, the air supply system 400 may optionally include anadditional air cooler (not shown) between the air cooler 456 and theintake manifold 114.

INDUSTRIAL APPLICABILITY

During use, the internal combustion engine 110 operates in a knownmanner using, for example, the diesel principle of operation. Referringto the exemplary air supply system shown in FIG. 1, exhaust gas from theinternal combustion engine 110 is transported from the exhaust manifold116 through the inlet duct 126 and impinges on and causes rotation ofthe turbine wheel 128. The turbine wheel 128 is coupled with the shaft130, which in turn carries the compressor wheel 134. The rotationalspeed of the compressor wheel 134 thus corresponds to the rotationalspeed of the shaft 130.

The exemplary fuel supply system 200 and cylinder 112 shown in FIG. 2may be used with each of the exemplary air supply systems 100, 300, 400.Compressed air is supplied to the combustion chamber 206 via the intakeport 208, and exhaust air exits the combustion chamber 206 via theexhaust port 210. The intake valve assembly 214 and the exhaust valveassembly 216 may be controllably operated to direct airflow into and outof the combustion chamber 206.

In a conventional Otto or diesel cycle mode, the intake valve 218 movesfrom the second position to the first position in a cyclical fashion toallow compressed air to enter the combustion chamber 206 of the cylinder112 at near top center of the intake stroke 406 (about 360° crankangle), as shown in FIG. 4. At near bottom dead center of thecompression stroke (about 540° crank angle), the intake valve 218 movesfrom the first position to the second position to block additional airfrom entering the combustion chamber 206. Fuel may then be injector fromthe fuel injector assembly 240 at near top dead center of thecompression stroke (about 720° crank angle).

In a conventional Miller cycle engine, the conventional Otto or dieselcycle is modified by moving the intake valve 218 from the first positionto the second position at either some predetermined time before bottomdead center of the intake stroke 406 (i.e., before 540° crank angle) orsome predetermined time after bottom dead center of the compressionstroke 407 (i.e., after 540° crank angle). In a conventionallate-closing Miller cycle, the intake valve 218 is moved from the firstposition to the second position during a first portion of the first halfof the compression stroke 407.

The variable intake valve closing mechanism 238 enables the engine 110to be operated in both a late-closing Miller cycle and a conventionalOtto or diesel cycle. Further, injecting a substantial portion of fuelafter top dead center of the combustion stroke 508, as shown in FIG. 5,may reduce NO_(x) emissions and increase the amount of energy rejectedto the exhaust manifold 116 in the form of exhaust fluid. Use of ahigh-efficiency turbocharger 320, 420 or series turbochargers 120, 140may enable recapture of at least a portion of the rejected energy fromthe exhaust. The rejected energy may be converted into increased airpressures delivered to the intake manifold 114, which may increase theenergy pushing the piston 212 against the crankshaft 213 to produceuseable work. In addition, delaying movement of the intake valve 218from the first position to the second position may reduce thecompression temperature in the combustion chamber 206. The reducedcompression temperature may further reduce NO_(x) emissions.

The controller 244 may operate the variable intake valve closingmechanism 238 to vary the timing of the intake valve assembly 214 toachieve desired engine performance based on one or more engineconditions, for example, engine speed, engine load, engine temperature,boost, and/or manifold intake temperature. The variable intake valveclosing mechanism 238 may also allow more precise control of theair/fuel ratio. By delaying closing of the intake valve assembly 214,the controller 244 may control the cylinder pressure during thecompression stroke of the piston 212. For example, late closing of theintake valve reduces the compression work that the piston 212 mustperform without compromising cylinder pressure and while maintaining astandard expansion ratio and a suitable air/fuel ratio.

The high pressure air provided by the exemplary air supply systems 100,300, 400 may provide extra boost on the induction stroke of the piston212. The high pressure may also enable the intake valve assembly 214 tobe closed even later than in a conventional Miller cycle engine. In thepresent invention, the intake valve assembly 214 may remain open untilthe second half of the compression stroke of the piston 212, forexample, as late as about 80° to 70° before top dead center (BTDC).While the intake valve assembly 214 is open, air may flow between thechamber 206 and the intake manifold 114. Thus, the cylinder 112experiences less of a temperature rise in the chamber 206 during thecompression stroke of the piston 212.

Since the closing of the intake valve assembly 214 may be delayed, thetiming of the fuel supply system may also be retarded. For example, thecontroller 244 may controllably operate the fuel injector assembly 240to supply fuel to the combustion chamber 206 after the intake valveassembly 214 is closed. For example, the fuel injector assembly 240 maybe controlled to supply a pilot injection of fuel contemporaneous withor slightly after the intake valve assembly 214 is closed and to supplya main injection of fuel contemporaneous with or slightly beforecombustion temperature is reached in the chamber 206. As a result, asignificant amount of exhaust energy may be available for recirculationby the air supply system 100, 300, 400, which may efficiently extractadditional work from the exhaust energy.

Referring to the exemplary air supply system 100 of FIG. 1, the secondturbocharger 140 may extract otherwise wasted energy from the exhauststream of the first turbocharger 120 to turn the compressor wheel 150 ofthe second turbocharger 140, which is in series with the compressorwheel 134 of the first turbocharger 120. The extra restriction in theexhaust path resulting from the addition of the second turbocharger 140may raise the back pressure on the piston 212. However, the energyrecovery accomplished through the second turbocharger 140 may offset thework consumed by the higher back pressure. For example, the additionalpressure achieved by the series turbochargers 120, 140 may do work onthe piston 212 during the induction stroke of the combustion cycle.Further, the added pressure on the cylinder resulting from the secondturbocharger 140 may be controlled and/or relieved by using the lateintake valve closing. Thus, the series turbochargers 120, 140 mayprovide fuel efficiency the air supply system 100, and not simply morepower

It should be appreciated that the air cooler 156, 356, 456 preceding theintake manifold 114 may extract heat from the air to lower the inletmanifold temperature, while maintaining the denseness of the pressurizedair. The optional additional air cooler between compressors or after theair cooler 156, 356, 456 may further reduce the inlet manifoldtemperature, but may lower the work potential of the pressurized air.The lower inlet manifold temperature may reduce the NO_(x) emissions.

An air and fuel supply system for an internal combustion engine inaccordance with the exemplary embodiments of the invention may extractadditional work from the engine's exhaust. The system may also achievefuel efficiency and reduced NO_(x) emissions, while maintaining workpotential and ensuring that the system reliability meets with operatorexpectations.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the disclosed air and fuelsupply system for an internal combustion engine without departing fromthe scope or spirit of the invention. Other embodiments of the inventionwill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. It isintended that the specification and examples be considered as exemplaryonly.

1. A variable compression ratio internal combustion engine, comprising:an engine block defining at least one cylinder; a head connected withsaid engine block, including an air intake port, and an exhaust port; apiston slidable in each cylinder; a combustion chamber being defined bysaid head, said piston, and said cylinder; an intake manifold; an airintake valve controllably movable to open and close the air intake port;an air supply system including at least one turbocharger fluidlyconnected to the air intake port; a fuel supply system operable tocontrollably inject fuel into the combustion chamber at a selectedtiming; and a variable intake valve closing mechanism configured to keepthe intake valve open by selective operation of the variable intakevalve closing mechanism. 2-23. (canceled)